In a power system, there is generally provided some limits or protections to prevent the power system circuit from electric or thermal damages. However, a power system usually suffers the protection point trade off issue as the power system works. If the protection point is choused higher limit in consideration of the process bias, the power system would be put in danger. But if a lower limit is choused, it would limit the system performance.
For more clear illustration, FIG. 1 shows a functional block diagram of a conventional protection scheme for a power system. A protection arrangement 10 is connected to an external power control circuit 12 and a power system 14, and the power control circuit 12 provides an input voltage VIN as the power source for the protection arrangement 10. The power system 14 comprises a main circuit 142, including for example reference voltage generator and amplifier, and a power stage 144 driven by the main circuit 142 to produce a regulated output voltage and an output current. Three protection circuits are provided in the protection arrangement 10, in which the current limit circuit 102 and the temperature sensor 104 are arranged parallel to control the main circuit 142 and limit over current condition and over thermal condition, and the under voltage circuit 106 will generate an error flag 146 to warren the power system 14 for under voltage condition. As shown in this example, the protection circuits 102, 104, and 106 in the protection arrangement 10 may use reference voltage REF provided by the main circuit 142 as bias control signals. The current limit circuit 102 monitors the output current of the power system 14 and provides a current limit signal VTRI1 for signaling the main circuit 142 once the output current is detected to hit a predetermined threshold, by which the main circuit 142 may adjust the current level and thus prevents the power system 14 from over current damage. The temperature sensor 104 monitors the working temperature of the power system 14 and provides a thermal protection signal VTRI2 for signaling the main circuit 142 once the temperature is detected to hit a predetermined threshold, in order to prevent the power system 14 from over thermal damage. The under voltage circuit 106 monitors the output voltage of the power system 14 and provides an under voltage signal VTRI3 to produce the error flag 146 once the output voltage is detected to hit a predetermined threshold, so as to adjust the output voltage level.
However, predetermined settings for the over current protection for the current limit circuit 102 and for the thermal protection for the temperature sensor 104 would be affected because of the process bias in the hardware of the protection arrangement 10. For example, a thermal protection condition is typically set between 150° C. to 170° C., but it could be down to 130° C. due to the process bias, and thus results in the power system 14 operating abnormally as in higher temperature. If a higher thermal protection condition is set for solving the process bias problem, the power system 14 may be burned-out in over thermal condition; but if a lower thermal protection condition is set, the performance of the power system 14 will decrease. The over current protection has the same problem.
Unfortunately, conventional protection circuits are all focusing on passive protections and therefore, they can only protect the power system but not improve the performance of the power system. It is thus desired an integrated protection for a power system with maximum system performance and reduced process bias.